Normal pregnancy is characterized by a remarkable enhancement of uterine blood flow due to vasodilation and growth and remodeling of uterine vasculature that is associated with an increased uterine reactivity to vasoconstrictors. The long-term goal of this proposal is to understand the causes and cellular mechanisms underlying the modulation of uterine vascular contractility during gestation, with a specific focus on the role of ion channels in endothelial and vascular smooth muscle cells. Our central hypothesis is that pregnancy down- regulates the delayed rectifier and Ca2+-activated potassium channels with a resultant increase in Ca 2+ influx and smooth muscle contractility. Enhanced Ca 2+ sensitization of contractile process is a synergistical mechanism. Pregnancy-induced up-regulation of PKC and RhoA is proposed as a common regulatory mechanism for enhanced Ca 2+ sensitization and inhibition of K+ channel function. These adaptive changes are counteracted by increased Ca2+-dependent production of endothelium-derived NO and EDHF. Furthermore, we suggest that the effects of pregnancy are highly localized by the side of placentation and are mediated by estrogen. Specific Aim 1 will determine the mechanisms that regulate a steady state global [Ca2+]_ in smooth muscle of uterine resistance arteries, and their modulation in pregnancy. The role of PKC and RhoA in regulation of Ca 2+ sensitization and ion channel function will be studied. Specific Aim 2 will explore the mechanisms by which NO and EDHF mediates the effects of pregnancy on uterine arterial contractility with a specific focus on the role of endothelial intracellular Ca 2+ and small conductance Ca 2+-activated potassium channels. Specific Aim 3 will test the role of local vs. systemic factors, and of estrogen in mediating the effects of pregnancy on uterine artery function. The three Specific aims will integrate the physiological function (regulation of arterial diameter) with intracellular (Ca 2+ signaling, Ca 2+ sensitivity and ion channel function) and molecular (PKC and RhoA) mechanisms and will be accomplished by direct measurements of arterial diameter, intracellular Ca, membrane potential, expression and distribution of PKC and RhoA, and ion currents in endothelial and smooth muscle cells. The proposed study will provide new insights into cellular and molecular mechanisms mediating the effects of pregnancy and estrogen on uterine blood flow and significantly deepen the understanding how these mechanisms are altered in pregnancy-induced hypertension and preeclampsia.